Linking birthdate with functional diversity in CA1 pyramidal neurons in the awake mouse hippocampus

细胞类型多样性通常反映了不同脑区神经元功能的可用库。海马体处理多模态信息，对空间和陈述性记忆功能很重要。在空间探索过程中，所有海马体子区的主要细胞都受到theta嵌套的gamma振荡的牵引，形成共同活动神经元的瞬态集合（Buzsaki和Draguhn 2004）。这些共同活动的神经元形成了顺序的激活模式，最终代表了动物在空间中的轨迹（OKeefe和Reece 1993）。在睡眠期间，这些序列通过锐波纹波振荡被重新激活以达到巩固的目的（Wilson 1994）。神经元集合的组织需要一个结构元素。不同类型的细胞可能携带神经元群，协调依赖状态的振荡，从而构建不同的网络功能。到目前为止，海马体中的细胞多样性似乎是gaba能细胞的主要标志（Klausberger 2008）。它们的活动被证明与不同的网络状态相关，并且部分植根于它们的时空胚胎起源。相比之下，只有少数研究表明谷氨酸能CA1锥体细胞可能包括几种具有不同遗传、形态和功能特征的亚型，尽管它们代表了80%的神经元群体。此外，Cossart实验室发现，在体外实验中，海马CA3区谷氨酸能神经元的早期时间起源描绘了一种独特的形态功能亚型（Marissal 2012）。我的项目旨在了解海马亚区CA1中海马谷氨酸能神经元的发育命运与神经元网络动力学之间的关系。我的项目是基于来自Cossart小组的转基因小鼠系（Allene 2012），其中转录因子Neurogenin2 （Ngn2）允许根据其出生日期标记谷氨酸能神经元。我将在急性海马切片中进行电生理记录，以表征CA1中早期出生（胚胎第11天）和晚期出生（胚胎第15天）神经元的基本电生理特性。此外，我想确定这些细胞在清醒的老鼠在跑步机上跑步时的生理活动模式。利用双光子钙成像，一种立体定向传递的遗传编码钙指示剂（GCaMP-6）将显示CA1背侧子场的单个焦平面内的单个动作电位。因此，我将监测几个锥体细胞在典型的行为相关的网络振荡（探索-嵌套的伽马和清醒不动/睡眠-尖锐波纹）中的放电模式，并研究它们在网络振荡中的招募。研究结果将为研究发育命运如何影响网络招募和网络动态提供重要的见解。

Cell type diversity classically reflects the available repertoire of neuronal functions in different brain regions. The hippocampus processes multimodal information and is important for spatial and declarative memory function. During spatial exploration, principal cells of all hippocampal subfields are entrained by a theta-nested gamma oscillation, forming transient assemblies of co-active neurons (Buzsaki and Draguhn 2004). These co-active neurons form sequential activation patterns which finally represent the animal´s trajectory through space (OKeefe and Reece 1993). During sleep these sequences are re-activated for consolidation purposes by sharp-wave ripple oscillations (Wilson 1994) . The organization of neuronal assemblies requires a structuring element. Different cell types probably entrain neuronal groups, coordinate state-dependent oscillations and therefore structure the various network functions. So far, cell diversity in the hippocampus seems to be a major hallmark for GABAergic cells (Klausberger 2008). Their activity was shown to be correlated to different network states and is partly rooted in their spatio-temporal embryonic origin. In contrast, only few studies address the possibility that glutamatergic CA1 pyramidal cells may comprise several subtypes with different genetic, morphological and functional features although they represent 80% of the neuronal population. In addition, the Cossart lab has found that an early temporal origin delineates a distinct morpho-functional subtype of glutamatergic neuron in the CA3 region of the hippocampus (Marissal 2012) in vitro.My project aims to understand the relationship between developmental fate and neuronal network dynamics of hippocampal glutamatergic neurons in the hippocampal subfield CA1. My project is based on a transgenic mouse line from the Cossart group (Allene 2012) where the transcription factor Neurogenin2 (Ngn2) permits the labeling of glutamatergic neurons according to their birthdate. I will perform electrophysiological recordings in acute hippocampal slices to characterize basic electrophysiological properties of early-born (embryonic day 11) and late-born (embryonic day 15) neurons in CA1. In addition, I want to determine physiological activity patterns of these cells in awake mice running on a treadmill. Using 2-photon calcium imaging, a stereotactically delivered, genetically-encoded calcium indicator (GCaMP-6) will indicate single action potentials within a single focal plane of the dorsal CA1 subfield. Thereby, I will monitor firing pattern of several pyramidal cells during typical behaviorally-relevant network oscillations (exploration - theta-nested gamma and waking immobility/sleep - sharp wave ripple) and investigate their recruitment into network oscillations.The results will provide important insights into how developmental fate affects network recruitment and network dynamics.